1. Field of the Invention
This invention relates to hydraulic lash adjusters used in the valve trains of internal combustion engines and the like, and more particularly to hydraulic lash adjusters of the self-contained type in which the fluid is sealed within the assembly with no provision for its replenishment from any external source during operation.
2. Description of the Prior Art
In the valve trains of internal combustion engines a predetermined valve clearance is generally provided in order to compensate for thermal expansion of various parts in the valve trains. However, since excess lash may be generated due to the valve clearance in the valve trains during engine operation, hydraulic lash adjuster have been used for automatically taking up the valve clearance in the valve trains, thereby preventing the possible lash and stabilizing the opening and closing operation of an engine intake or exhaust valve.
Conventional hydraulic lash adjusters compensate for fluid leakage by means of supplying pressurized fluid to the interior of the lash adjusters through a passageway in the cylinder block. However, there have been disadvantages that the passageway through which pressurized fluid flows is complicated in construction, and that the operation comes to be unstable due to changes in viscosity of pressurized fluid. In order to eliminate such disadvantages hydraulic lash adjusters of the self-contained type are being provided, which are not fed from an external source of hydraulic fluid but rather contain their own source of such fluid.
In the conventional hydraulic lash adjuster of the self-contained type, however, there have been still various drawbacks that the mechanism compensating for the fluid leakage is imperfect, that the operation comes to be unstable due to the entrapment of air in the fluid, and that the mechanism of the lash adjuster is quite complicated and expensive to manufacture.